hero: calculate movements with fractional fixed point coordinates

[jorgegv]

The current movement uses integer calculations for coords and increments. This if fine for Horiz or Vert movement, but when moving diagonally it moves much faster. E.g. for DX=1 and DY=1, if we move Horiz or Vert (only) X or Y are incremented by 1, speed is 1 pixel per time unit. But if we move diagonally, X and Y are simultaneously incremented by DX=1 and DY=1, and the speed is then 1.41 pixels per time unit, which is 41% faster.

This can be avoided if we keep the movement coordinates and increments as 16-bit fixed point values (8 bit integer + 8 bit decimal), and also increments according to directions are adjusted for the diagonal moves (e.g. DX = 1 if moving Horiz, but DX = DY = 0.71 if moving diagonally).

Fixed Point math should be done in base 256 for best precision.

Update:

• Use Fixed Point coordinates for hero movement.
• Add DX_BOTH and DY_BOTH increments, used when moving in H and V direction simultaneously. Calculate as DYsin(W) and DXcos(W), being W = arctan(DY/DX). Precalculate in DATAGEN and generate FP fractional values ready to use (no trig calculations in realtime!)